Method of preparing plates for electromechanical engraving



Jan. 29, 1963 w. D. M LEAN 3,075,395

METHOD OF PREPARING PLATESEFOR ELECTRWMECHANICKL ENGRAVING Filed Feb.15, 1960 COLOR TREATED SURFACE TREATED SURFACE INVENTOR. WILLIAM D. MACLEAN BY fleayuanyum A T TORNEYS 1 reproduction becomes more of a blacksmear.

aired rates This is a continuation in part of my co-pending applicationNo. 561,172, filed January 24, 1956, now abandoned.

This invention relates to the method of treating the surface of aluminumplates to adapt the plates to be engraved for use in letter pressprinting. More particularly, the invention is directed to a method ofoxidizing aluminum plates to provide a porous, skin hard surface whichis readily receptive to a dye and which can be easily engraved in anelectronic-mechanical engraver.

The plates to which the present invention is directed are screenprocessed, that is, the plates are provided with regularly spaced dots,the dots being formed by cutting conical depressions in the surface ofthe plate. The depressions each vary in size depending on the varyinggradations of light and dark of the photograph or the like to bereproduced so as to permit sharp half-tone reproduction.

The plates, prepared in accordance with the invention, are screenprocessed in an electronic-mechanical engraver. An engraver of this typeis known as the Klischograph and is disclosed in Patent No. 2,863,000.

To prepare an engraved plate from a photograph, the Klischographprovides a photo-electric scanner which passes back and forth across thephotograph to be reproduced and a stylus which passes back and forthover the plate to be engraved. The photo-electric scanner receivessignals of varying amplitude depending upon the gradations of light anddark in the photograph being scanned. These signals are transmitted tothe stylus and the stylus in turn pierces the surface of the plate tovarying depths in accordance with the amplitude of the signal receivedfrom the photo-electric scanner.

The Klischograph and other like machines were originally developed to beused with plastic plates. As such the usefulness of the machine islimited. Plastic plates do not have the lasting qualities for goodreproduction. Al-

though the sharpness and tone quality may be satisfactory inreproduction from plastic plates, the number of acceptable reproductionsthat 'can be made is limited.

Plastic tends to absorb ink so that after 30,000 to 40,000

reproductions, substantially all the detail is lost and the A plasticplate is of no use in producing mats for stereotypes or for similaradaptions of this character wherein impressions are required from theengraved plates. Such plastic plates are only good for a short run butwill not stand the pounding and pressure. Furthermore, such platescannot be routed or corrected as are metal plates.

The principal difiiculty in adapting the machine for use with metalplates is the difliculty in providing an inexpensive metalwhich can beengraved without wearing out the stylus of the engraving machine. As aconsequence, the electro-machanical engravers have continued to be usedfor plastic plates and metal plates are still being processed byexpensive chemical engraving processes.

An object of the present invention is to provide a metal plate for usewith electro-mechanical engraving machines. Aluminum is a desirablemetal in that it is comparatively inexpensive and generally has thephysical characteristics necessary for use in electro-mechanicalengraving. Aluminum, in its untreated state, however, is soft and, whenmechanically engraved, results in the production of burrs.

" ice On the other hand, when the surface of the aluminum is oxidized byconventional methods, the resultant surface is so hard that the stylusor engraving tool tends to wear out before a single plate can beengraved. The coating is too hard and stressed so that it chips ratherthan cuts.

It is, therefore, another objective of the invention to provide a methodof treating aluminum for use in electromechanical engraving machines,the process imparting a comparatively soft, porous oxide surface to thealuminum so that the complete plate can be engraved without wearing outthe stylus.

In the engraving process it is necessary for good engraving results andend products to provide plates having a colored surface. With a coloredsurface the operator of the engraving machine may determine at a glancethe desired quality of the reproduction he is developing. The operatorcan from such an inspection of a colored surface make whateveradjustments are necessary in the machine to correct or overcome thedeficiency, such as controlling the depth of cut.

It is still another objective of the invention to provide a process offorming an oxide on the surface of an aluminum plate to provide a poroussurface that is readily receptive to a coloring dye. The surface of thealuminum prepared in accordance with the present invention willsatisfactorily receive the dye up to five times as fast as conventionaldyeing processes.

Other objectives of the invention will become more readily apparent fromthe following detailed description of the invention taken in conjunctionwith the accompanying I drawings in which:

FIG. 1 is a perspective view of a plate prepared in accordance with theinvention, and

FIG. 2 is a cross-sectional view taken along lines 2-2 of FIG. 1.

The principal feature of the process by which the desiredcharacteristics of the surface of an aluminum plate are obtained are thecomparatively high current density and short time of applying thecurrent during the formation of the oxide on the aluminum plate.According to conventional anodizing processes, the anodizing currentdensity is normally in the range of 10 to 20 amps. per square foot, thecurrent being applied from between 15 to 60 minutes. In accordance withone form of the applicants process, an alternating current of 180 amps.per square foot is applied for 60 seconds to produce the desired surfacecharacteristics. In another form of the applicants invention a directcurrent of approximately 50 amps. per square foot is applied for 8minutes.

Broadly, the process comprises the following steps: (1) Clean thesurface of the aluminum plate.

(2) Rinse.

(3) Form an oxide on the plate using a high current density applied fora comparatively short time in a sulfuric acid solution.

(4) Rinse.

(S) Immerse in a dye solution for minutes, at F. to F.

(6) Rinse in cold water.

(7) Immerse in water maintained at a temperature of at least but belowthe boiling point.

approximately 5 More specifically, the process comprises the forming ofan oxide coating and dyeing of 38 H 14 alcan designation aluminum whichhas been rolled, scalped and homogenized.

These plates in the first instance are cut to oversize dimensions andare then individually set out and/or supported upon racks and are heldby one or more spring clips constructed of aluminum material that engagean excess plate section. The thus supported plates are then immersed ina cleaning and degreasing solution or other means adapted for theremoval of all surface held dirt or impurities and more specifically toremove all the grease or drawing compound that may be present on the rawsheet stock.

The cleaning step may be carried out in one of several procedures, butthe present method contemplates the use of non-etching chlorinatedsolvents or non-etching hydrocarbon solvents. As an example, a cold bathis prepared with carbon tetrachloride to remove all surplus oils orgreases together with other foreign materials. An immersion time ofsixty seconds is normally adequate for this operation and if necessary,the work may be wiped with a cloth to remove marking ink that stillremains upon the surface of the plates. Ordinary commercial carbontetrachloride is employed in this cold soak. While the minimum time of aminute is given above for the immersion time, the plates may be soakedfor two or three minutes in the carbon tetrachloride bath, but thetemperature of this bath is held at 70 F. during the cleaning cycle.

In place of the above solvents there are other nonetching cleaners andcleaning agents (used hot or cold) that may be employed to clean themetal. Primarily, however, it is preferable to use any of thechlorinated or hydrocarbon solvents that can be formulated into soakingbaths or that may be permissibly used as vapor cleaning media ininstances where the work is supported in vapors that are being drivenout of the solutions through the application of heat. Petroleum solventscan be used as a cold soak bath, but these latter solvents-are not toodesirable because of the fire hazards that such solvents create.

Upon removal of the cleaned plates from the degreasing bath, the rackedarticles or plates are then rinsed in cold running water 2 or 3 secondstogether with agitation of the work. This rinse is to remove any foreignmatter that may still cling or adhere to the metal plate surfaces. Thetime of rinse is not critical and actually the step consists of an inand out operation in subjecting the work or plates to this rinse.

The work is now taken and immersed with the racks into an electrolyticoxidizing tank. The electrolyte consists of a 50% aqueous solution byweight of sulphuric acid operated and maintained at a temperature of 70F. The solution is gently agitated by an air agitation system. In thisbath the work or plates are made one electrode of an A.C. current sourceand the other electrode is a graphite member. A current density of 180amperes per square foot is utilized, while the operating voltage mayvary from 12 to 18 volts as may be determined by the surface area beingsubjected to the load and its relative location in the tank. The timerequired for this operation is 60 seconds.

Should aluminum be used for both electrodes, and the graphite electrodeis omitted, the voltage is increased to approximately twice the valuethat was being impressed with the aluminum graphite combination ofelectrodes. The first method is preferred although the latter can beused if desired, depending upon conditions of operation.

While the preferred current density is 180 amps. per square foot, acurrent density in the range of 225 a.s.f. to 135 a.s.f. will besatisfactory. The time for application of the current should becorrespondingly reduced to 45 seconds or increased to 90 seconds as thecurrent density is increased or decreased.

In an alternative form of the oxidizing process, the plates are immersedin an 18% solution of sulfuric acid maintained at a temperature of 110F. A direct current of 50 amps. per square foot is applied forapproximately 8 minutes at a voltage of 12 volts. The current could bedecreased to 40 est. or increased to 60 a.s.f. and produce asatisfactory surface. If the current is decreased below 50 amps. persquare foot or increased above 50 amps. per square foot, the time ofapplication of the current should he correspondingly increased ordecreased within the range of 12 minutes to 5 minutes.

The rack with its plates is now transferred from the electrolytic bathinto a rinse bath by immersion into cold running water to removesulphuric acid. This is a straight immersion step and need only take 2to 5 seconds. More than one water rinse is advisable.

After rinsing, the rack and its plates are then immersed into a dye tankas a single dip operation to apply color to the surfaces of the sheetplates. The dye tank solution utilized is prepared with suitable dyecolor selected from one of the water soluble aniline dye groups. Forexample, if a violet color is to be applied, the dye used may be anEloxan Violet 5 BL, a product so specified under dyes produced by GeigyDyestuffs. Dye concentrations vary, but with the dye named, the solutionconcentration is made with 5 grams of this dye used per liter of water.The dye solution is heated and maintained at a temperature ranging fromF. to F. A minimum immersion time of 5 minutes is maintained, whilegentle air agitation is provided for the dye tank solution. If a darkercolor is desired, more dye concentrationcan be employed or the worlgorplates may be left longer in the dye, tank solution.

Another example-of a dye tank color solution is to provide five (5)grams of water soluble aniline dye, such as anthraquinone blue selectedfrom the group of water soluble anthraquinone dyestuffs, or Colour IndexNo. 246 selected from the group of water soluble-disazo dyestufis', orColour Index No. 758 selected from the group of water soluble xanthenedyestuffs, dissolved in one litre of water and with the solution beingoperated and maintained at a temperature of 150 F. to 165" F. with aminimum sheet immersion period of 5 minutes. The Colour Index numbersgiven are those found in the Colour Index of the Society of Dyers &Colourists.

The plates will take on the color over the surfaces thereof and when thecolor concentration or tone blend desired is reached, the rack andplates are Withdrawn from the dye tank and rinsed. The rinse step hereis conducted by a dip or immersion into a bath of cold running waterover a period of several seconds to wash away and to remove all excessdyefrom the surfaces of the aluminum plates.

A second final rinse step is then used by transferring the plates into arinse tank having water heated to at least 'a temperature of F. but notto the boiling point.

This rinse is carried on for 15 to 20 seconds so as to prevent streaksand spots, and also, to dry the plates upon removal from this bath asbrought about through the inherent latent heat taken on by the metalplates during the immersion rinse. This last rinse solution must not beheated to the boiling point, since this would tend to seal the coatingdeveloped under the treatment previously given to the plates.

When this last step has been brought to conclusion, the racked platesare removed from the racks and they may be finally trimmed and packagedfor shipment in 25 piece lots in boxes or in cartons with 100 plates tothe carton and in selected size lots of 5" x 6", 6" x 8", or 8 x 10" orgreater for engraving purposes. An individual plate treated according tothis method is illustrated on the accompanying drawing forming a part ofthis specification.

Having described my invention, I claim:

1. The process of reproducing indicia having gradations of light anddark on an engraving plate for letter press printing purposes,comprising the steps of forming an oxide coating on the surface of analuminum sheet to produce a surface having the soft, porouscharacteristics of an aluminum surface produced by immersing the sheetas one of two electrodes in a 70 bath of 50% by weight solution of H 80;and applying a voltage of 12-18 volts for one minute between electrodesto provide 180 amperes per square foot at the surface of said sheet,mechanically piercing the surface of said sheet at regularly spacedpositions throughout the surface of said sheet to provide regularlyspaced dots throughout the surface of said sheet, and electronicallyvarying the depth of each cut in accordance with the gradations of lightand dark of the indicia to be reproduced.

2. The process of reproducing indicia having gradations of light anddark on an engraving plate for letter press printing purposes,comprising the steps of electrolytically forming an oxide on the surfaceof an aluminum sheet to produce a soft, porous surface by immersing thesheet as one of two electrodes in a 70 F. bath of a 50% by weightsolution of H 50 and applying an alternating current voltage of 12 to 18volts for one minute between electrodes to provide 180 amperes persquare foot at the surface of said sheet, mechanically piercing thesurface of said sheet at regularly spaced positions throughout thesurface of said sheet to provide regularly spaced dots throughout thesurface of said sheet, and electrically varying the depth of each cut inaccordance with the gradations of light and dark of the indicia to bereproduced.

3. The process of reproducing indicia having gradations of light anddark on an engraving plate for letter press printing purposes,comprising the steps of electrolytically forming an oxide on the surfaceof an aluminum sheet to produce a soft, porous surface by immersing thesheet as one of two electrodes in a 110 bath of 18% by Weight solutionof H 80 and applying a direct current voltage of 12 volts forapproximately eight minutes between electrodes to provide approximately50 amperes per square foot at the surface of said sheet, mechanicallypiercing the surface of said sheet at regularly spaced positionsthroughout the surface of said sheet to provide regularly spaced dotsthroughout the surface of said sheet, and electronically varying thedepth of each cut in accordance with the gradations of light and dark ofthe indicia to be reproduced.

References Cited in the file of this patent UNITED STATES PATENTS1,869,041 Bengston July 26, 1932 2,084,685 Hogner June 22, 19372,691,627 Johnson Oct. 12, 1954 2,863,000 Hell et a1 Dec. 2, 19582,901,412 Mostyvich et a1 Aug. 25, 1959

1. THE PROCESS OF REPRODUCING INDICIA HAVING GRADATIONS OF LIGHT ANDDARK ON AN ENGRAVING PLATE FOR LETTER PRESS PRINTING PURPOSES,COMPRISING THE STEPS OF FORMING AN OXIDE COATING ON THE SURFACE OF ANALUMINUM SHEET TO PRODUCE A SURFACE HAVING THE SOFT, POROUSCHARACTERISTICS OF AN ALUMINUM SURFACE PRODUCED BY IMMERSING THE SHEETAS ONE OF TWO ELECTRODES IN A 70* BATH OF 50% BY WEIGHT SOLUTION OFH2SO4 AND APPLYING A VOLTAGE OF 12-18 VOLTS FOR ONE MINUTE BETWEENELECTRODES TO PROVIDE 180 AMPERES PER SQUARE FOOT AT THE SURFACE OF SAIDSHEET, MECHANICALLY PIERCING THE SURFACE OF SAID SHEET AT REGULARLY